1. Field of the Invention
The present invention relates to an aircraft having a sweepforward main wing with composite major structural members.
2. Description of the Relevant Art
Aircraft are limited to certain configurations to meet necessary aerodynamic requirements or due to mechanical strength limitations on structural members. For example, a main wing is generally swept back to reduce the wave resistance or drag, increase the drag critical Mach number, i.e., the speed at which the drag coefficient starts to increase sharply, or reduce fluctuations of the center of pressure, i.e., the point at which the line of action of a resultant aerodynamic force intersects the wing chord, due to a velocity difference. The sweepback angle also serves to locate the main wing aerodynamic center in an appropriate position.
Sweepforward wings are also employed to optimize the main wing aerodynamic center. Sweepforward wings are free of tip stall which would tend to occur with swept wings, do not allow the effectiveness of ailerons to be lowered at low speeds, and are capable of avoiding undesirable flight characteristics such as pitch-up due to tip stall caused by a sweepback angle. However, sweepforward wings are disadvantageous in that they are possibly subject to twists called torsional divergence in a high speed range.
For the reasons described above, present aircraft generally have a main wing swept backward.
To permit the crew and passengers to easily board and deplane an aircraft or to load the cargo on and unload the cargo from an aircraft with ease, it is effective to employ relatively short landing gear struts. If the landing gear is retractable, then shorter landing gear struts are advantageous in that any space for storing the landing gear in the fuselage may be smaller, allowing the fuselage to have a larger effective storage capacity. However, the shorter landing gear struts pose the following problems:
The shorter landing gear struts necessarily position the main wing and the engine nacelles closely to the runway surface. If an aircraft with shorter landing gear struts takes off or lands with an angle of bank, then the wing tips are liable to contact the runway surface. Accordingly, aircraft with shorter landing gear struts are necessarily required to have other wings than low wings. However, in the case where the main wing of an aircraft is not low wings, an attachment structure for attaching the main wing to the fuselage imposes limitations on the space in the cabin, making passengers uncomfortable, or results in aerodynamically undesirable conditions.
More specifically, the joint between a main wing and a fuselage passes through the cabin in a longitudinal position of the airframe which is based on the relative relationship of the aerodynamic center and the center of gravity of the fuselage to meet demands for static stability and balanced condition of the aircraft. If the wing-fuselage joint structure is disposed in the cabin, then the space capacity of the cabin is reduced. If the wing-fuselage joint structure is disposed on the fuselage above the cabin, then the drag coefficient of the airframe is increased, and the drag is increased due to an increase in the frontal area of the airframe.
The cabin is given a comfortable passenger space if the wing-fuselage joint is positioned in a rear portion of the cabin. However, it is necessary to optimize the aerodynamic center with the wing-fuselage joint thus positioned. Specifically, if the wing-fuselage joint is positioned in a rear portion of the cabin, then since the aerodynamic center is shifted backward with a sweepback angle, it is necessary to install a canard in the vicinity of the nose of the airframe for thereby shifting the aerodynamic center in the forward direction. If a canard is employed, however, certain structural disadvantages occur, i.e., the structural members of the nose on the front end of the fuselage must be reinforced, and the space for installing accessories in the nose is reduced. Furthermore, the canard induces undesirable flight characteristics. For example, the aircraft is caused to pitch down due to stall of the canard, and to pitch up when the main wing is in the wake of the canard.